As far as I know, you can't actually hook up a VCR to a Firewire port - VCRs
only create analog output. You might be able to run the VCR into your TV
Tuner card's composite video in jacks. Similarly, if you have a Digital
Video camcorder, you may be able to hook it to the Firewire and hook the VCR
to it.
You might want to look at www.papajohn.org in the section on importing
analog video.